In American courts (and probably all justice systems based on English common law), a "dying declaration" is an exception to the rule barring hearsay statements. A dying declaration is a statement made made while the declarant believed that his death was imminent (he doesn't actually have to die) and it must relate to the cause or circumstances of what he believed to be his impending death.

It is not a wide-open opportunity to admit evidence of all self-serving statements made upon one's death bed - it is limited to statements about the cause or circumstances of death. In addition, the courts do not assume the statements are true - just that a trier-of-fact (jury or judge) can consider the statements.

Having studied my family tree and the false legends that get passed down from generation to generation, I give no credence to stories perpetuated or concocted as death nears.